The invention generally relates to remote medical patient monitoring. More particularly, it involves real-time communication of patient data, and especially waveform data, over a single telephone line concurrently with both medical practitioner and patient voice.
Increasingly, medical patients are provided with portable, patient-proximate monitoring and control equipment that, in turn, is connected to a remote (typically centralized) health-care provider, e.g. a physician, skilled technician or other service provider. Typically, patient vital sign data, e.g. an electrocardiograph (ECG) waveform, is digitized and transmitted over a phone line to the remote monitoring site for diagnostic, oversight and recording purposes. Conventionally, digital transmission protocols for use on voice-grade communications channels such as the public switched telephone network (PSTN) or cellular telephone network (CTN) use the entire available bandwidth for data transmission. This precludes the use of the phone for voice interaction between the physician and the patient.
To make the patient feel at ease, it is important to both the patient and the physician to interact the way they would during an office visit. Such interaction provides the physician with an opportunity to follow up any observations with questions to help diagnose the condition of the patient, as well as to offer reassurances and any needed instruction regarding in the patient's use of the monitoring equipment. Similarly, it is important that the voice and patient data are transmitted in real-time so the medical practitioner is able to correlate the patient's activities and comments with the transmitted patient data. For example, a patient may be in a variety of psychological and physiological states that affect the data being collected, which otherwise may appear abnormal or otherwise significant when it is analyzed by a practitioner who does not know this event occurred while the data was being collected. Similarly, equipment problems also may lead to data which appears to reflect significant or life-threatening patient conditions, but can be identified and remedied almost immediately if the practitioner is in real-time communication with the patient.
To further explain the need for real-time measurement and communication of patient data concurrently with physician and patient voice, it is necessary to differentiate real-time voice communication with underlying, delayed data communication from systems that concurrently transmit real-time voice and real-time data. As discussed in more detail below, a system that uses a single telephone line for real-time voice communication between physician and patient while previously measured and stored data is transmitted, or interleaved, in the available bandwidth is dramatically different from a system that enables concurrent real-time voice and real-time data communication over a single communication line. The first enables the physician and patient to interact and respond to each other, as well as the physician to receive patient data while this interaction is occurring. The limitation of this system, however, is that the patient is receiving and viewing patient data which is not synchronized with the interaction between the physician and the patient. Instead, data is measured, stored and transmitted in available bandwidth, which can result in a defined duration of data taking much longer than that time duration to be transmitted and received. Unless the patient voice and data are synchronized, the physician is unable to correlate the received patient data with the patient's current bodily activities, mental state and physical condition.
Similarly, it is necessary to discuss the concept of "real-time" communication of voice and data. As discussed subsequently, this term appears to be used fairly loosely in other references to describe communication that occurs over a common communication link, without concerns or import given to the time lapse between the time data is collected from a patient and the time the data is received by a diagnostician, or to pauses or other system-required delays between communications. As used herein with respect to the present invention, it should be understood that real-time communication is meant to refer to virtually instantaneous transmission, which preferably means less than one second between the capture and transmission of the data and voice. Less preferably, but still within the scope of this term are communications which take up to a few seconds. Anything beyond this, such as 10 seconds, a minute, sixty minutes, etc. is not considered to be real-time communication, as used herein.
The requirements for a system to transmit concurrently this synchronized, real-time voice and data are further identified and distinguished when the patient data is waveform data. By way of background, U.S. Pat. No. 5,012,814 to Mills et al. for an implantable-defibrillator pulse detection-triggered ECG monitoring method and apparatus describes the characteristics, including duration and principal components, of a typical ECG waveform. The disclosure of Mills et al. is hereby incorporated by reference. In Mills et al., a typical ECG waveform, which includes a recurrent portion (centrally shown in the illustrated trace) commonly referred to as a QRS complex, and implantable cardio-verter/defibrillator (pacemaker) pulse are shown, respectively, in FIGS. 3A and 3B. In column 5, lines 28-49, the typical duration of the waveform and pulse are discussed. Specifically, the QRS complex may last for up to 100 milliseconds, while a typical pacemaker pulse lasts only a few milliseconds.
Therefore, to record and transmit either of these waveforms in a continuous, graphical representation, a patient monitoring system must be capable of measuring, recording and transmitting data taken in sufficiently small increments, or preferably continuously, to permit the waveform, including any and all peaks, troughs or aberrations therein, to be accurately reconstructed or traced. The method and apparatus disclosed herein satisfies this requirement, as discussed subsequently, with its capability for graphical waveform data and at least one-way voice communication to be simultaneously transmitted in real-time over a single telephone line. The data is measured at a sufficiently high frequency (time resolution) and accuracy (amplitude resolution) to allow the patient's vital sign waveform to be reproduced, or "traced," after transmission for diagnosis and analysis by the practitioner. Such frequency and accuracy requirements are in compliance with applicable known standards such as ANSI/AAMI EC-11, EC-13, EC-38 and SP10; IEC1099; etc., familiarity with which is assumed.
Therefore, to transmit real-time, or synchronized, patient data and single or duplex voice communication over a single communication line, a system not only must be able to measure monitoring and/or diagnostic quality waveform data so that it can be reproduced after transmission, but also must be able to synchronize this data with single or duplex voice communication over the limited bandwidth of a single communication line. Several recent patents have attempted to address these problems, yet as discussed, fail to allow concurrent, real-time transmission of voice and monitoring or diagnostic quality waveform data over a single communication line.
For example, U.S. Pat. No. 5,553,609 to Chen et al. is entitled "Intelligent Remote Visual Monitoring System for Home Health Care Service." Chen et al. disclose a system for home health care monitoring which includes a Slave Monitoring Station 26 utilizing a personal computer and modem 76 for digitizing and communicating voice and patient information to a remote Master Monitoring Station 24 over a single telephone line, as shown in FIG. 7. The patient data consists of video images taken by camera 68, and the patient audio is detected by microphone 72. The video images and the audio are compressed digitally at one station and then decompressed at the other to reduce the bandwidth during communication.
The system of Chen et al., however, is only capable of sampling or measuring at rates of up to 15 frames per second. This rate may be suitable for freeze-frame video images, however grainy and jerky, but it will not suffice to communicate patient waveform data to a medical practitioner. For example, if a typical ECG waveform, with a QRS complex lasting less than 100 milliseconds, was measured at a rate of 15 samples per second, no more than two samples could be taken over the entire QRS complex. Furthermore, if this data were presented in a graphical, time-dependent format, the intermittent, spaced-apart readings would likely omit vital information necessary to diagnose specific medical conditions, such as tachycardia and ischemia. In addition, a practitioner would often be unable to determine which waveform a particular sample came from because of the missing transition regions between readings. Perhaps this is why Chen et al. disclose replacing the video equipment with medical sensors that only detect static or averaged values, such as weight, body temperature and pulse rate, which are relatively stable and may be adequately measured and communicated using the sampling rate provided by the system of Chen et al. These static or relatively static measurements are not waveform data, much less diagnostic waveform data. Because only video clips or averaged, static data values are measured and transmitted by the system of Chen et al., this perhaps also explains why Chen et al. do not disclose any form of meaningful error detection with respect to the measured data.
Similarly, U.S. Pat. No. 5,544,661 to Davis et al. is entitled "Real Time Ambulatory Patient Monitor" and discloses a cellular system for monitoring patient waveform data, comparing the data to stored threshold values and contacting a central monitoring station if the measured data exceeds the threshold values. If so, the system establishes communication with the central station and transmits the previously measured data to the station while allowing two-way communication between the station and the patient. Despite its title, however, the patent to Davis et al. only discloses and enables real-time voice communication, with the stored buffer of patient data being interleaved to fit within any remaining bandwidth for transmission to the central station.
The system disclosed by Davis et al. measures patient data, including 3-lead ECG and plethysmograph, compares the data to stored threshold values and stores the data in a sixty minute buffer. If the data exceeds the threshold value, the system activates a cellular unit and establishes communication with the central station. Once this communication is established, two-way voice communication between the patient and the station is possible, while the previously stored data is multiplexed and interleaved with the voice communication. As shown in FIG. 9, the patient's data is measured, then compressed and stored in a one hour buffer, where it can be accessed if needed. FIG. 11 demonstrates how the stored, prerecorded data is multiplexed and interleaved with the two-way voice communication to let the practitioner see the data that was collected before communication was established between the practitioner and the patient. While the data may not be days or even hours old, it is not "real-time" data, which requires measurement and transmission within seconds of each other. The data is minutes or even an hour or more old when transmitted to the central station. Therefore, there is no correlation with the patient's current physical state or condition, and it will not be possible to explain data which may have resulted simply from a patient experiencing an excited or elevated psychological or physiological state, or from the life signs equipment malfunctioning or becoming disconnected from the patient. Furthermore, when the data is not transmitted in real time or synchronized with the voice communication, such communication is much easier and less demanding on the already limited bandwidth of a single communication line. This is largely because the data can be stretched or spread out to transmit over a longer period of time to reduce the bandwidth necessary at any given moment to transmit the data.
Furthermore, the system of Davis et al. provides no detection for erroneously measured data. As discussed, if the measured data exceeds previously set baseline values, the system automatically establishes communication with a central station to open a two-way voice channel between the patient and the central station and to transmit the data. The measured data is stored within various buffers until transmitted to the central station or discarded. Each of the buffers is used to store different measurements, which are subsequently and separately compared to respective stored threshold values to determine if a life-threatening condition exists. As shown schematically in FIGS. 13 and 14 and explained in col. 7, line 50 to col. 8, line 38, of Davis et al., the buffers each store a different type of information. Specifically, as indicated at 1407 in FIG. 14, each buffer stores data relating to one of the following groups: S-T deviation, QRS width and rate, T wave amplitude and polarity, plethysmograph rate and amplitude. Each of these different measurements or values are then compared to separate, stored threshold values at 1408 in FIG. 14. If the measured value is greater than the threshold value, then the monitoring station is notified using a cellular connection. Besides the fact that the buffers disclosed in Davis et al. provide no protection against erroneous data, the entire system disclosed in Davis et al. neither describes nor suggests any mechanism for detecting erroneously measured or recorded data. Therefore, if the data stored in any one of the previously discussed buffers is erroneous, it could cause the system to alert the monitoring station, which in turn will erroneously alert the patient that the patient may be in a life-threatening situation. This false alarm to the patient may in fact trigger an actual medical emergency in the patient. This alone demonstrates why the invented error detection technique disclosed herein represents a significant improvement over conventional patient monitoring systems.
Thus, it is a principal object of the present invention to provide at least for concurrent digital medical patient data and voice communication over a single, duplex communication line.
It is another object of the invention to provide such digital and voice communication over the public switched telephone network (PSTN).
Yet another object is for such communication to include the communication of patient waveform data.
Still another object is to provide such communication within real-time limits of when the patient data is obtained.
Another important object of the invention is to provide such communication with high data and voice integrity.
Yet another object is to render the communication link's bandwidth automatically dynamically allocable to variable demand as between data and voice.
It is another object of the invention to provide also for the communication over such a line of digital video information in real time at a useful refresh rate.
Another object is to provide combined voice channels over the same single physical channel on which medical patient data is carried.
Still another object of the invention is to provide for the communication of medical patient data that is synchronized with the patient's voice communication to the practitioner.
Briefly, the invented apparatus enables patient waveform and other data to be measured and concurrently transmitted in real-time with at least one-way voice communication between the medical practitioner and the patient over a single, usually common, communication line. In preferred embodiments of the apparatus, two-way concurrent voice and data communication is established. Patient life signs equipment at the patient site is connected to the patient and to a DSVD device having the ability to digitize and compress the patient's voice and having the ability to decompress and render in analog form the physician's voice via a standard telephone. A modem modulates and demodulates transmitted and received data over the telephone line. At a remote monitoring site a second modem receives and transmits data over the same telephone line. The second modem is connected with a second DSVD device connected to a display- or printer-equipped receiving station for presentation of the patient waveform or other data, e.g. in the form of an ECG trace, in textual or graphic form to a remote service provider. Thus, the service provider has the ability to overview patient life signs data obtained while in direct vocal communication with the patient. The data and voice are synchronized and transmitted in real time, enabling the physician to account and correct for the patient's current physical or emotional state, as well as for instructing the patient or otherwise reassuring the patient of the proper use of the life signs monitor or diagnosing or prescribing in real time a response to what is learned from the monitored data.
These and other objects and advantages of the invention will be more clearly understood from a consideration of the accompanying drawings and the following description of the preferred embodiment.